moy-fp/src/Relation/difference.js

A functional programming library.

import curry from '../Function/curry'
import toString from '../String/toString'

/**
 * [a] -> [a] -> [a]
 */
const difference = curry(
  (list2, list1) => {
    const differenceObj = {},
          delimiter = String.fromCharCode(0),
          result = []
    for(let item of list2){
      differenceObj[
        Object.prototype.toString.call(item) +
        delimiter +
        toString(item)
      ] = true
    }
    for(let item of list1){
      if(!differenceObj[
        Object.prototype.toString.call(item) +
        delimiter +
        toString(item)
      ]){
        result.push(item)
      }
    }
    return result
  }
)

export default difference